The present invention relates to an apparatus and method for washing a substrate for cleansing a surface of a substrate such as a semiconductor wafer or an LCD substrate.
In the manufacturing process of a semiconductor device such as an LSI, a surface of a semiconductor wafer is strictly required to be maintained at a high cleanliness. To meet this requirement, a surface of a wafer is washed every time the wafer is subjected to any treatment or both before and after the treating process. In, particularly, the photolithography step, it is absolutely necessary to wash the surface of the wafer. The washing treatment of the wafer surface is carried out by a scrub-washing apparatus disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 57-102024 or Japanese Patent Disclosure No. 62-259447. In the scrub-washing apparatus, a rotary brush is brought into contact with a wafer surface while applying a washing liquid to the wafer surface. Also, the rotary brush is moved at a predetermined speed along the wafer surface from a central portion toward a peripheral portion of the wafer so as to remove contaminants attached to the wafer surface.
However, the contaminants attached to the wafer surface are not necessarily distributed uniformly over the entire wafer surface. For example, these contaminants may be concentrated in a central portion or in a region of the peripheral portion of the wafer. Therefore, the contaminants tend to remain in the heavily contaminated portion even after the washing treatment. If the washing time is simply increased in an attempt to overcome this difficulty, the region of high cleanliness tends to be degraded in cleanliness. The decrease in cleanliness of the originally clean region is considered to be derived from the fact that the rotary brush itself generates contaminants.